Restoring a Johnson CD-12, 1955 5-1/2

[steelespike]

Re: Restoring a Johnson CD-12, 1955 5-1/2

Sometimes the rings get carboned up and stick.A good decarb treatment with something like sea foam may free things up.
Just follow the directions.Also could be a head gasket.

 

[HighTrim]

Re: Restoring a Johnson CD-12, 1955 5-1/2

That is low, you can try a decarb but Im thinking you ll be pulling the head, changing the gasket and dressing the head.

 

[Bwana Don]

Re: Restoring a Johnson CD-12, 1955 5-1/2

the low numbers are a cause for concern......are you using a screw in tester or a rubber tipped press in type?

Screw in tester. It seems to be sealed good too. I did the test three times, I was thinking of the Green Bay Packers when I was doing it to. We love the Packers in Detroit! All three tests I got the same #, 30 pounds.

It's a Harbor Freight tester, maybe I should try to check it for accuracy. It is brand new though and looks decent.

 

[Bwana Don]

Re: Restoring a Johnson CD-12, 1955 5-1/2

That is low, you can try a decarb but Im thinking you ll be pulling the head, changing the gasket and dressing the head.

I'm a Machininist/Engineer so I'm not afraid to lap in the head or change a gasket. I've got access to a machine department which is nice. Grinders, mills, lathes, polishing equipment, sandblaster, cnc mills etc... the works. Not to mention inspection equipment. I know how to use it all to.

 

[1946Zephyr]

Re: Restoring a Johnson CD-12, 1955 5-1/2

I would try a different compression guage and see if the numbers are still consistant. If so, then I would pull the head. You might have a bad head gasket.

 

[jmendoza]

Re: Restoring a Johnson CD-12, 1955 5-1/2



My CD-11(1954) was in far worse condition than either of those engines above, it had no decals and was painted olive drab, transom bracket clamp screws seized, carb was corroded inside, all the rubber lines were rotten, very low compression (25 PSI). It had thrown a rod and busted the crankcase (was JB welded back by someone), but it ran when I squirted some gas in the carb. One of the first things I did was to remove the head, clean the carbon off the piston crowns and combustion chambers, and replaced the head gasket. I cannot complain however, the engine was a gift to me from a friend. Today, it's a fine runner, and all I did was run some Valv Tect through the top end to get the compression back.

 

[1946Zephyr]

Re: Restoring a Johnson CD-12, 1955 5-1/2

LOL those CD's are tough to kill.

 

[64osby]

Re: Restoring a Johnson CD-12, 1955 5-1/2

BD - Thanks for posting about the low compression, and everyone else on what to do.

It reminded me to tested mine and compression was low - 25 ish, tried the PB, no help, off came the head and gasket, it was a shot.

Minor Hijack Over.

Hope you have better luck than mine, but it's an easy fix.

 

[Bwana Don]

Re: Restoring a Johnson CD-12, 1955 5-1/2

Stop in anytime 64. I read your thread on the Lone Star, I like it. 14' boats are my favorite, small and personable yet able to take some waves.

I keep meaning to bring the compression gage into the shop and plug it in to an airline. I forget, wait I'm going to get it now. OK it's in the cab of my truck. I'll try to check it tomorrow (Friday) for accuracy. It's probably accurate and I'll be into the head. From what everyone says these motors are nearly indestructible though. Probably a gasket or some carbon, we'll see. I'm pumped about this little motor.

 

[64osby]

Re: Restoring a Johnson CD-12, 1955 5-1/2

............... I'm pumped about this little motor.

You should be, It will look great on Zack's boat, or is this a kicker for yours?

 

[Bwana Don]

Re: Restoring a Johnson CD-12, 1955 5-1/2

You should be, It will look great on Zack's boat, or is this a kicker for yours?

It's going on the Sea Scamp. I've got a QD-16, 10 horse for the Offshore.

Well I took the Harbor Freight compression gage into the shop yesterday. I clamped a hose to the end of it, hooked up a regulator and it checked out, reads right on the money. I repeated with a second regulator (with gage) and it checked out too. Gage is accurate, compression in this motor is low.

For $20 the Harbor Freight Compression Gage is a major value.

 

[64osby]

Re: Restoring a Johnson CD-12, 1955 5-1/2

It's going on the Sea Scamp. I've got a QD-16, 10 horse for the Offshore.

..............gauge is accurate, compression in this motor is low.

For $20 the Harbor Freight Compression Gage is a major value.

That will be great on the Scamp. I had a 7.5 one lung on my 12'er, pushed it pretty good but it wasn't smooth like a 2 cylinder.

The head and gasket should go easy, I did spend about 3 hours getting my head and block cleaned up and flush, good luck.

Might have to look at that gauge, the two I have are probably 50 years old. A screw in would make life easier.

 

[nwcove]

Re: Restoring a Johnson CD-12, 1955 5-1/2

head gasket is an easy job, unless the bolts are seized.....dont be afraid to give it some penetrating fluid a day before you wrench on it. (are there many/any mechanical differences between the cd 12, and cd 13/14? )

 

[1946Zephyr]

Re: Restoring a Johnson CD-12, 1955 5-1/2

The CD13 is a completly different design than the 10's, 11's and 12's. The CD13 and later had the re-designed midsection with the rubber shock mounts.

 

[Bwana Don]

Re: Restoring a Johnson CD-12, 1955 5-1/2

OK I'm back on the CD-12. I've got a few projects lined up and I'm not finishing them. This one has moved to the forefront. After this the QD-16 and then the 1958 5-1/2 horse. The 58 I got free as a parts motor with the cd-12. It looks complete and re-buildable!

I've started a tear-down to determine the cause of low compression. We are also replacing the consumables in the ignition; coils, condensers, points, wires and plugs. Impeller will also be replaced.

Pictures will follow and I've got some questions. I found some very interesting things in the tear-down. Off to photobucket I go.

Cheers guys,
Don

 

[Bwana Don]

Re: Restoring a Johnson CD-12, 1955 5-1/2

Here's the top of the motor.


These look new, don't they? Should I still replace them?

 

[Bwana Don]

Re: Restoring a Johnson CD-12, 1955 5-1/2

More pics;


Magneto plate off.


Carb off and is rebuilt;

 

[Bwana Don]

Re: Restoring a Johnson CD-12, 1955 5-1/2

I lapped the surface on the glass top of the kitchen table.


Here's the head gasket. It's split in the middle, this would explain the low compression.


Pistons cleaned up;

 

[Bwana Don]

Re: Restoring a Johnson CD-12, 1955 5-1/2

OK I tried to take a picture of the bore but it's hard to see. There;s some minor pitting at the top of one bore.


What are my options? I do have a brand new set of rings. Opinions are welcome. This motor is getting traded for a 14' Starcraft Holiday! Yea baby. It was originally going on the 12' Sea Scamp but that boat is sold. This motor will be a troller for the St. Clair River. I'll be fishing with the guy too so I want it to idle down nice . I need to do a respectable job.

Is this minor pitting, (.005 deep aproxamatly) going to hurt anythhing? Should I break the glaze and then re-ring????

Thanks for you time guys.

 

[nwcove]

Re: Restoring a Johnson CD-12, 1955 5-1/2

coils are new, but i would remove that electrical tape and see if theres enough wire to cut/solder/heat shrink the spot that got chaffed by the flywheel. i would also move the green wire so its tucked back away from the points. i would put the head back on and see what the comp numbers look like before splitting the block to re-ring it. jmo